Diagnosis & Testing

When servicing the ABS-VI, the following steps should be followed in order. Failure to follow these steps may result in the loss of important diagnostic data and may lead to difficult and time consuming diagnosis procedures.

Connect a bi-directional scan tool, as instructed by the tool manufacturer, then read all current and historical diagnostic codes. Be certain to note which codes are current diagnostic code failures. DO NOT CLEAR CODES unless directed to do so.

Using a bi-directional scan tool, read the CODE HISTORY data. Note the diagnostic fault codes stored and their frequency of failure. Specifically note the last failure that occurred and the conditions present when this failure occurred. This last failure should be the starting point for diagnosis and repair.

Perform a vehicle preliminary diagnosis inspection. This should include:

Inspection of the ABS hydraulic modulator for any leaks or wiring damage.

Inspection of brake components at all four (4) wheels. Verify no drag exists. Also verify proper brake apply operation.

Inspection for worn or damaged wheel bearings that allow a wheel to wobble.

Inspection of the wheel speed sensors (where possible) and their wiring. Verify correct air gap range, solid sensor attachment, undamaged sensor toothed ring, and undamaged wiring, especially at vehicle attachment points. The sensors for the rear wheels are built into the rear wheel hub/bearing assemblies and cannot be inspected or serviced.

Verify proper outer CV-joint alignment and operation.

Verify tires meet legal tread depth requirements.

If no codes are present, or mechanical component failure codes are present, perform the automated modulator test using the Tech 1®, T-100® or equivalent scan tool, to isolate the cause of the problem. If the failure is intermittent and not reproducible, test drive the vehicle while using the automatic snapshot feature of the bi-directional scan tool.

Perform normal acceleration, stopping, and turning maneuvers. If this does not reproduce the failure, perform an ABS stop, on a low coefficient surface such as gravel, from approximately 30-50 mph (48-80 km/h) while triggering any ABS/ETC code. If the failure is still not reproducible, use the enhanced diagnostic information found in CODE HISTORY to determine whether or not this failure should be further diagnosed.

Once all system failures have been corrected, clear the ABS codes. The Tech 1® and T-100®, when plugged into the Data Link Connector (DLC), becomes part of the vehicle's electronic system. The Tech 1® and T-100® scan tools can also perform the following functions on components linked by the Serial Data Link (SDL):

Display ABS data

Display and clear ABS trouble codes

Control ABS components

Perform extensive ABS diagnosis

Provide diagnostic testing for intermittent ABS conditions

Each test mode has specific diagnostic capabilities which depend upon various keystrokes. In general, five (5) keys control sequencing: YES, NO, EXIT, UP arrow and DOWN arrow. The FO through F9 keys select operating modes, perform functions within an operating mode, or enter trouble code or model year designations.

In general, the Tech 1® has five (5) test modes for diagnosing the anti-lock brake system. The five (5) test modes are as follows:

MODE F1: CODE HISTORY
-In this mode, fault code history data is displayed. This data includes how many ignition cycles since the fault code occurred, along with other ABS information. The first five (5) and last fault codes set are included in the ABS history data.

MODE F2: TROUBLE CODES
-In this test mode, trouble codes stored by the EBCM, both current ignition cycle and history, may be displayed or cleared.

MODE F3: ABS SNAPSHOT
-In this test mode, the Tech 1® captures ABS data before and after a fault occurrence or a forced manual trigger.